Wear behaviour of thermally oxidised tool surfaces as low-friction separation layers for dry sheet metal forming

This paper presents the results and analysis of wear investigations carried out on a wear test bench with high strength sheet metal DP600+Z drawn over selectively oxidised α-Fe2O3 tool steel surfaces. Wear investigations were carried out with several selectively oxidised specimens by varying the pulling and counter force, and thus the surface pressure on the samples. This allowed for a systematic study of the wear behaviour of the oxide layers under different loads. The specimens were characterised using microscopy (light microscopy, scanning electron microscopy and topography analysis) and scratch testing on a nanoindenter. The study shows that it is possible to realise a dry metal forming process while using α-Fe2O3 oxide layers on the tool steel surface. The oxidised surface acts as a friction reducing separation layer and protects the tool against wear. Simultaneously, it was found that the surface of sheet metal drawn over oxidised specimens showed lower zinc abrasion than sheet metal drawn over non-oxidised reference specimens at the same surface pressure. In addition, the oxidised specimens have a reduced Zn pick-up affinity.